There are many circuit applications requiring a boosted voltage (i.e., a voltage boosted above a predetermined operating voltage level for the circuit) to ensure that the circuit operates as intended even though there may have been unknown process, operating voltage or temperature variations. The boosted voltage is typically generated by a voltage boosting circuit, which is also sometimes referred to as a voltage booster.
FIG. 1 illustrates a conventional boosting circuit 10. The illustrated boosting circuit 10 includes a pre-charge circuit 12, boosting capacitor 14, parasitic capacitor 16 and a load capacitor 18. A positive electrode of the boosting capacitor 14 is connected to the pre-charge circuit 12. A negative electrode of the boosting capacitor 14 is connected to receive a boost voltage Vboost used to boost-up the pre-charge voltage. The parasitic and a load capacitors 16, 18 are connected to a node between the connection of the positive electrode of the boosting capacitor 14 and the pre-charge circuit 12.
In operation, to generate a high boosted final output voltage Vfinal, the boosting capacitor 14 is pre-charged to a predetermined voltage (Vprecharge) by the pre-charge circuit 12. The voltage at the negative electrode of the boosting capacitor 14 is then raised to a higher voltage (e.g., Vboost) so that a voltage appearing at the positive electrode of the boosting capacitor 14 is higher than the pre-charge voltage.
Because the parasitic capacitor 16 and the load capacitor 18 share the charges of the boosting capacitor 14, the final boosted voltage Vfinal will be less then the Vprecharge+Vboost voltages applied to the boosting capacitor 14. That is,
                              Vfinal          =                      Vprecharge            +                                          C_boosting                                  (                                      C_boosting                    +                    C_parasitic                    +                    C_load                                    )                                            ⨯              Vboost                                      ,                            (        1        )            where C_boosting is the capacitance of the boosting capacitor 14, C_parasitic is the capacitance of the parasitic capacitor 16, and C_load is the capacitance of the load capacitor 18.
The prior art boosting circuit 10 has some drawbacks. For example, in the situations when the capacitances of the parasitic and load capacitors 16, 18 cannot be precisely calculated, the final boosted voltage Vfinal cannot be accurately predicted. Furthermore, any undesired leakage current at the positive electrode of the boosting capacitor 14 will cause charge loss and will change the expected final boosted voltage Vfinal. In addition, any unwanted capacitive coupling to the positive electrode of the boosting capacitor 14 will also alter/lower the final boosted voltage Vfinal. All of these drawbacks are undesirable.
Accordingly, there is a desire and need for a voltage boosting circuit in which the accuracy of the boosting circuit (with respect to the final boosted voltage) is ensured and predictable and does not suffer from the drawbacks found in the prior art boosting circuits (e.g., boosting circuit 10).